1. Field of the Invention
The present invention relates to an information reproducing apparatus, and more particularly to an apparatus which can realize a system operable to reproduce one type of information along with a plurality of channels of the other type of information at the same time, for example, a multilingual system operable to reproduce a video and a plurality channels of audio at the same time.
2. Related Art
In recent years, a DVD has been widely spread and a video and audio reproducing system using the DVD has been introduced into an aircraft or a museum where there is a situation in which a large audience can enjoy the same video picture. In this situation, each audience does not always understand the same language.
Meanwhile, in the DVD, according to a DVD-Video standard, one stream (“multiplexed stream”) is recorded as one set of program, in which one channel of video stream, plural channels (up to eight channels) of audio streams corresponding to the video stream, and plural channels (up to thirty-two channels) of sub-picture streams are multiplexed. Thus, it is possible to introduce the DVD system as the multilingual system which can supply the audio corresponding to the language that each audience can understand in the aforementioned situation.
Furthermore, as for the use in the aircraft, a movie which has not been yet played at movie theaters is sometimes played. In this case, there has been strongly demanded a system that is implemented with a copyright protection which can prevent illegal distribution of contents of the movie before release, or trace the source of the distribution even if the contents are illegally distributed.
As a basic idea of the copyright protection, the following method is generally used. In order to prevent the contents from being illegally distributed, the contents are encrypted, and video data to be reproduced is embedded with reproduced date and time, a reproduced media ID, a device ID for reproduction and a content ID containing copyright information such as a title, a producer or the like by digital watermarking and so on which enables the source of the illegal distribution to be traced.
Conventionally, as the video and audio reproducing apparatus implementing the multilingual system using the DVD, the system disclosed in Japanese Patent Laid-Open Publication No. 11-164257 or 8-31096 for example is known. The Publication No. 11-164257 discloses a multilingual system which includes a plurality of audio decoders arranged in parallel each extracting an audio stream of the corresponding language from audio data in presentation data produced from the DVD with reference to navigation data produced from the DVD and decoding the respective audio stream. The Publication No. 8-31096 discloses that audio data is distributed according to stream ID of audio data, decoded by the corresponding decoder, and output to a predetermined signal channel.
In general, the present video and audio reproducing apparatus using the DVD is configured so that one audio selected from the plural audios are output to one video. An AV decoder which include a plurality of decoders as one chip so as to output a plurality channels of audio signal to one video signal at the same time has not been generally used. Therefore, the aforementioned multilingual system is achieved by arranging in parallel a plurality of widely-spread and commercially available inexpensive AV decoders each having one video decoder and one audio decoder.
FIG. 6 illustrates a configuration of a conventional audio and video reproducing apparatus (AV reproducing apparatus) which allows the multilingual system to have the aforementioned copyright protection function.
A stream data reproducing section 100 reproduces a multiplexed stream in which compressed video information and a plurality of channels (first to n-th channel (n is a natural number)) of compressed audio information are multiplexed.
Since the multiplexed stream reproduced by the stream data reproducing section 100 has been encrypted (encryption such as Triple-DES) to protect a copyright, a decryption section 101 decrypts the cipher applied to the multiplexed stream reproduced by the stream data reproducing section 100.
A first stream decoder (AV decoder) 102 decompresses the decrypted multiplexed stream.
A video management information embedding section 103 embeds reproduced date and time, a disc ID, a device ID, a content ID and the like in video data extended by the first stream decoder 102.
A video output section 104 generates a reproduction video signal from the video data embedded with the video management information. The reproduction video signal is output to the outside through a video output terminal 105.
A first audio output section 106 generates a reproduction audio signal based on the first audio data decompressed by the first stream decoder 102. The reproduction audio signal is output to the outside through an audio output terminal 107.
Second to n-th stream decoders 108 to 110 decompress the multiplexed stream input to the first stream decoder 102 in the same manner as that of the first stream decoder 102. Second to n-th audio output sections 111 to 113 generate reproduction audio signals according to the second to n-th audio data decompressed by the second to n-th stream decoders 108 to 110, respectively. Each reproduction audio signal is output to the outside through each of audio output terminals 114 to 116.
By user's selecting any one of the first to n-th audio output terminals 107 and 114 to 116, the audio regarding the language which the user selects and can understand is supplied to a headphone or the like of the user.
According to the conventional AV reproducing apparatus having the above configuration, during audio and video reproducing operation, the multiplexed stream decoded by the decryption section 101 in which video and audio are multiplexed is equally fed to all of the first to n-th stream decoders 102 and 108 to 110. In other words, the multiplexed stream which is in unprotected state after the decryption flows on all data bus lines connected to the second to n-th stream decoders 108 to 110. The data flow shown by arrows shown by thick lines in FIG. 6 is the multiplexed stream which is in the unprotected state after the decryption. Since the multiplexed stream in unprotected state flows on all the data bus lines connected to the second to n-th stream decoders 108 to 110, a risk of being illegally copied by extracting the multiplexed stream from these data bus lines can increase. Thus, it is necessary to protect all of the data bus lines by molding them with resin or the like in a circuit substrate of the reproducing apparatus.
As described above, it has been demanded to improve the security to protect the copyright further solidly regarding the branch of the decrypted multiplexed stream.